Four pairs of meroterpenoid enantiomers with coumarin- and chromone-monoterpene skeletons from Gerbera piloselloides and their bioactive activities

Abstract

Phytochemical investigations of the extracts from the whole plant of Gerbera piloselloides resulted in the isolation and identification of four pairs of previously unreported meroterpenoid enantiomers with coumarin- and chromone-monoterpene skeletons (1a/1b–4a/4b), including two pairs of 5-methylcoumarin monoterpenes and two pairs of 5-methylchromone monoterpenes. The structures and absolute configurations of these compounds were definitively determined through NMR and MS data, NMR calculation with DP4+ analysis, electronic circular dichroism (ECD) data, and X-ray diffraction analysis. Structurally, compounds 1–4 feature 5-methylphenylpropanoid-substituted monoterpene frameworks. All compounds were evaluated for neuroprotective activity and cytotoxicity against the human cancer cell line SGC-7901 in vitro. Compounds 1, 1a, and 1b exhibited inhibitory effects with IC₅₀ values ranging from 12.07 to 12.44 μM against SGC-7901 compared with the positive control vorinostat (IC₅₀ value 0.37 μM). Furthermore, the hypothetical biogenetic pathways for these compounds were discussed.